The Korean Central News Agency, the mouthpiece of the North Korean state, said the North Korean people were "burning with hatred" over the flights. The United States said the demonstration is meant to show resolve with South Korea.

Despite North Korean rhetoric threatening to unleash its nuclear arsenal, Klingner says recent North Korean troops movements make a more conventional attack in the near future a more likely scenario.

North Korean artillery units have moved closer to its border with South Korea and to five South Korean islands that North Korea has shelled in the past, Klingner said.

"There is a greater risk of miscalculation by Kim, a (greater) likelihood that South Korea would respond militarily to a North Korean attack," Klingner said. Together with military exercises on both sides of the border and everything else that has happened in the past month, "it's generating increasing concern about the situation on the Korean Peninsula," Klingner said.